Gas turbine engines on aircraft use the discharge force of gases for thrust to drive the aircraft. Braking forces may be obtained after landing or during flight by reversing the direction of the discharge.
Reverse thrust discharge involves a blockage of the rearward flowpath plus transfer of the axial gas flow to a radial flow. This radial flow has a forward component producing the reverse thrust.
U.S. Pat. No. 5,082,209 issued Jan. 21, 1992 to Andrew G. Keyser shows a plurality of reverser ducts extending outward from the central exhaust passage. A door sealing each duct is secured to a rotatable ring. The doors are rotated from the closed position to permit exhaust flow through the reverser ducts.
The doors which seal the entrance port to the reverser ducts must provide positive seal during normal forward thrust operation. These must continue to seal after completing numerous reverse thrust cycles. Wear and durability of the seal is therefore a major concern.